The present invention relates to ducts for containing cables, such as optical cables, and to methods for mounting such ducts in an enclosure or conduit.
In the telecommunications industry it is common practice to string cable through a duct, which has previously been placed in an outer conduit. The cable may be electrical, optical or any other type. In recent years, data transmission through optical cable has vastly expanded. As a result, there has been a great increase in demand for cable to carry the digital data. Existing conduits, both above and below ground, have been utilized for new ducts and cables. The old contents of the conduit, usually electrical cable, are removed and ducts are installed, through which optical cables are subsequently placed. U.S. Pat. Nos. 5,027,864 and 4,565,351, the contents of which are hereby incorporated by reference, are examples of this.
Existing conduits have a limited amount of interior space. Further, the conduits may extend along a tortuous path characterized by multiple bends and adjacent length portions extending in non-planar directions. They are usually circular in cross section and often are buried or otherwise not readily accessible. The ducts, which are placed in the conduits, usually have relatively rigid, circular cross-sections but are flexible along their length. Consequently, multiple ducts are difficult, if not impossible, to insert within conduits in some cases.
Using circular duct in a circular conduit is an inefficient utilization of space. That is, there is a considerable amount of wasted space between the circular ducts. For example, a conduit with a 4xe2x80x3 internal diameter would hold only three ducts with a nominal 1xc2xcxe2x80x3 internal diameter. This inefficient use of the conduit interior space or cross-sectional area corresponds with a low packing efficiency.
In further efforts to achieve cable installation efficiencies, consideration has been given to the mounting or stringing of cable within existing utility service lines such as gas or water lines. Such an installation technique would provide a low-cost cable pathway to a home or business. However, such utility service lines are typically not oversized for the volume of water or gas that they are intended to deliver and may only range in diameter from one to several inches. Accordingly, even though the cable conduit may be small in diameter, it would still occupy a significant volume and cross-sectional area of the service line and tend to interfere with the utility delivery.
In accordance with the present invention, ducts having a variable cross-sectional configuration provide pathways for cables. The variable cross-sectional configuration of the duct facilitates mounting of the duct in an enclosure or conduit and also enables increased numbers of ducts to be mounted in a given size conduit. The cable may be inserted in the duct prior to or after the duct is mounted within the enclosure or conduit.
The cross-sectional configuration of the duct may be varied between an extended condition of greater cross-sectional area and a contracted condition of lesser cross-sectional area. Typically, the duct is normally in the contracted condition and is manipulated to the extended condition as by fluid pressure.
The facilitating of duct mounting in a conduit relates to the reduced cross-sectional area of the duct in the contracted condition and also to the reduced cross-sectional profile of the contracted duct as well as the increased duct flexibility or conformability provided by the collapsible duct wall. That is, the varied degrees of duct bending required as the duct is moved along a tortuous path are more readily accommodated by the variable cross-sectional configuration and collapsible wall of the duct.
This invention includes a method of installing a cable in an inner pathway or duct. The duct has a collapsible wall which is movable between an extended condition and a contracted condition. The extended condition has a greater cross sectional area than the contracted condition. The duct is inserted, in the contracted condition, into an outer conduit. The duct is moved to the extended condition and the cable is inserted into the duct. The duct is subsequently moved to the contracted condition. The duct may also be used without an outer conduit.
This invention further includes a duct providing a pathway for a cable. The duct includes a collapsible wall movable between an extended condition and a contracted condition wherein the extended condition has a greater cross-sectional area than the contracted position. When the duct is in the extended condition it is suitable to have a cable passed through it longitudinally. When the duct is in the contracted position it may be placed in a conduit in greater numbers than an equivalent size of a non-collapsible duct.
This invention greatly enhances the efficiency of existing conduits. In this invention the ducts are made of a collapsible or flexible material. While the ducts are sturdy enough to remain intact when cable is passed through them, the ducts have a normally contracted configuration of reduced cross-sectional area and, for example, they may collapse under their own weight. That is, the ducts flatten themselves unless there is a force to open them, such as air pressure. In this invention, the flattened ducts are pulled or pushed, in a flattened state, through a conduit. In a 4xe2x80x3 internal diameter conduit there would be room for seven nominal 1xc2xcxe2x80x3 ID flattened ducts. This is over twice the number of rigid ducts of the same size.
When it is desired to place a cable in the duct, the duct is simply inflated. A source of air pressure, usually an air compressor, is connected to one end of the duct. The air pressure causes the duct to inflate to an expanded oval or circular cross section sufficiently large to permit a cable to pass through it. After the cable is inserted, that duct is deflated and another one is inflated. This process continues until all of the ducts have had a cable placed in them. The increase in capacity and efficiencies from this invention are obvious.
The size constraints that have heretofore inhibited the mounting of ducts in existing service lines or other pipelines are significantly lessened, if not overcome, by the collapsible ducts of the invention. That is, a greater number of cables may be contained in a smaller size duct and the cross-sectional area of the installed duct is itself reduced by collapsing the duct about the cables following installation. In this manner, a greater number of cables may be installed in a service line or pipeline with a minimal amount of flow reduction.